A light-emitting optoelectronic component is disclosed in U.S. Pat. No. 5,040,868, for example. It has a housing basic body, which surrounds by moulding two electrical conductor tracks of a leadframe and also has a recess in which an electromagnetic-radiation-emitting luminescence diode chip is electrically conductively and mechanically mounted. The recess is potted with a radiation-transmissive casting composition, by means of which a coupling-out of electromagnetic radiation from the luminescence diode chip is improved and the luminescence diode chip is protected from external influences.
Luminescence diode chips used in components of this type are subjected to certain manufacturing fluctuations during their production which often lead to fluctuations in the brightness of semiconductor chips of nominally identical type during the operation thereof. Both wafers that are produced in different epitaxy process runs and different wafers that are produced simultaneously in one process run are subjected to such manufacturing fluctuations, which in particular comprise fluctuations in epitaxy processes and doping processes.
It is an object of the present invention to provide an optoelectronic component of the type mentioned in the introduction which can be produced in a technically simple manner with a predetermined radiant intensity or luminous intensity. Moreover, the intention is to specify a method for producing optoelectronic components of this type.
This object is achieved by means of an optoelectronic component or a method in accordance with the independent patent claims. The dependent patent claims relate to advantageous embodiments and preferred developments of the component and of the method.
An optoelectronic component comprising a housing and a luminescence diode chip arranged in the housing is specified, which component emits an electromagnetic useful radiation. The housing has a housing material which is transmissive to the useful radiation. Said housing material is admixed with radiation-absorbing particles in a targeted manner for setting a predetermined radiant intensity or luminous intensity of the emitted useful radiation.
The wavelength spectrum of the useful radiation preferably comprises a range visible to the human eye. Accordingly, the luminous intensity of a useful light emitted by the optoelectronic component is preferably set by the radiation-absorbing particles.
In connection with the present application, the term “radiation-absorbing particles” is not to be understood to mean phosphors which are absorbent for a radiation in a first wavelength range that is emitted by the luminescence diode chip and are excited by this radiation to emit an electromagnetic radiation in a second wavelength range, which is different from the first wavelength range. In other words, the radiation-absorbing particles do not re-emit optical radiation when they have absorbed an electromagnetic useful radiation of the component. It is possible, however, for the radiation-absorbing particles not only to absorb but also in part to scatter the useful radiation.
The radiant intensity or luminous intensity emitted during the operation of the optoelectronic component is reduced in a targeted manner in a technically simple way by the radiation-absorbing particles. A reduction of the efficiency of the optoelectronic component is thus accepted in order to precisely set the radiant intensity or luminous intensity of said component independently of fluctuating radiant intensities or luminous intensities of the luminescence diode chips used.
A method for producing an optoelectronic component is specified, moreover, in which a luminescence diode chip is provided. The radiant intensity or luminous intensity emitted by the luminescence diode chip during the operation thereof is measured. In the case of a composition to be provided which is transmissive to the useful radiation and is also admixed with radiation-absorbing particles, the concentration of the radiation-absorbing particles is selected in a targeted manner depending on the measured radiant intensity or luminous intensity in order thereby to indirectly set a radiant intensity or luminous intensity to be obtained in the component. A further method step involves arranging the composition which is transmissive to the useful radiation in a beam path of the electromagnetic radiation emitted by the luminescence diode chip during the operation thereof.
The composition is expediently a curable composition into which the radiation-absorbing particles are mixed in the uncured state. The setting of a brightness to be obtained, that is to say a radiant intensity or luminous intensity of the component, requires, with the method specified, measuring the radiant intensity or luminous intensity emitted by the luminescence diode chip and also selecting the concentration of the radiation-absorbing particles depending on the measurement result. This can be carried out in a technically simple way and enables the brightness to be set very precisely.
The radiation-absorbing particles are advantageously absorbent for the entire wavelength spectrum of the useful radiation. In addition or as an alternative, they are advantageously absorbent for the entire wavelength spectrum of the radiation emitted by the luminescence diode chip during the operation thereof. Particularly preferably, the absorption coefficient of the radiation-absorbing particles varies by less than 10% in the entire spectrum of the useful radiation. In particular, in the relevant wavelength range the particles have a wavelength dependence of negligible magnitude in terms of the absorption. As a result, the brightness of the component can be reduced without significantly influencing the emission spectrum of the useful radiation.
In accordance with a further advantageous embodiment of the component, the housing material which is transmissive to the useful radiation has at least one phosphor. It has been established that precise setting of the brightness by means of the radiation-absorbing particles is possible in this case, too.
The radiation-absorbing particles particularly preferably have carbon black. Carbon black is generally known as a by-product in combustion processes. Moreover, it is produced industrially and used as a colorant, particularly as a reinforcing filler in automobile tyres. Carbon black generally has a relatively great wavelength dependence in terms of its absorption behaviour, which, in particular, also holds true for visible light. It has been established, however, that specific forms of carbon black have a very low wavelength dependence in terms of the absorption behaviour in the visible wavelength range.
Industrial carbon black is produced with various defined technical properties. Carbon black is present in the form of aggregates composed of a plurality of primary particles. In particular carbon black having particularly small primary particle sizes is suitable for a use as radiation-absorbing particles. Moreover, it is advantageous to use industrial carbon black with a compact aggregate structure. The expression “low structure carbon black” (LSCB) is used by experts for such types of carbon black. The aggregates preferably have an average extent of less than or equal to 1 μm.
In accordance with one expedient embodiment of the component, the radiation-absorbing particles are electrically insulating. It is thus possible for the housing material which is transmissive to the useful radiation to directly adjoin the luminescence diode chip without the risk of short-circuiting on account of electrically conductive particles. As an alternative, electrically conductive particles may also be used. If the concentration of the latter in the housing material is sufficiently low, the risk of short-circuiting can likewise be at least largely avoided. In this case, the maximum concentration depends on the aggregate size. With LSCB, which has a small aggregate size compared with customary carbon black particles, it is possible to use a higher concentration in association with the same risk of short-circuiting.
Generally, the radiation-absorbing particles advantageously have an average particle diameter of less than or equal to 100 nm (particle average). Such small particles can be dispersed particularly well in a housing material. In the case of carbon black, the primary particles of the agglomerates preferably have such a small average particle diameter.
The housing material which is transmissive to the useful radiation preferably has a casting composition or a moulding composition. With materials of this type, it is possible to produce housing parts of well-defined forms and dimensions. Casting compositions can be potted or moulded for example in an injection-moulding method. Moulding compositions can be processed in a transfer moulding method.
In one expedient embodiment, the housing material which is transmissive to the useful radiation has at least one of the materials from the group comprising epoxy resin, acrylate, silicone, thermoplastic and hybrid material with at least one of said materials.
In a further preferred embodiment, the luminescence diode chip is encapsulated or surrounded by the housing material which is transmissive to the useful radiation. In particular, it is possible for the housing material to directly adjoin the luminescence diode chip.
In one expedient embodiment, the component has a housing basic body with a housing cavity in which the luminescence diode chip is mounted. The housing cavity is at least partly filled with the housing material which is transmissive to the useful radiation. The housing cavity is preferably filled by potting with the composition which is transmissive to the useful radiation.
A further advantageous embodiment of the component provides for the component to have a housing body having an exterior area. The housing material which is transmissive to the useful radiation is applied at least to the exterior area of the housing body.
The housing material applied on the exterior area of the housing body may expediently be present in the form of a foil. The latter is fixed on the exterior area of the housing body for example by being laminated on or by means of an adhesive. The foil advantageously has a constant thickness. It is expediently embodied in flexible fashion. As an alternative, it is also possible for the thickness of the foil to vary. This can be realized for example by structuring a foil with constant thickness in a targeted manner.
In addition or as an alternative, it is also possible to use as housing material a foil which is admixed with radiation-absorbing particles.
A luminescence diode chip is specified whose exterior area is provided with a covering material which is admixed with radiation-absorbing particles in a targeted manner for setting a predetermined radiant intensity or luminous intensity of a useful radiation emitted by the luminescence diode chip. The covering material is preferably applied directly on the luminescence diode chip. The covering material is particularly preferably present in the form of a foil. The foil is fixed on the exterior area of the luminescence diode chip for example by being laminated on or by means of an adhesive. This may additionally be effected in the wafer assemblage, that is to say before a multiplicity of luminescence diode chips are singulated from a common assemblage.